Jet physics in electron–proton scattering

Hadronic jets in electron–proton collisions at HERAhave been used for some considerable time as a tool for tests of the theory of strong interactions, quantum chromodynamics. Using jet final states, basic concepts like the factorisation ansatz for cross-section calculations, the perturbative approach to the cross section and the universality of the proton partondistribution functions can be examined. More concretely, jet measurements provide ready access to the strong coupling of QCD, α s , and to the partondistributions. In this report, an overview of jet results from the HERAexperiments H1 and ZEUS and their interpretation is given together with a description of the theoretical foundations of jet physics in electron–proton collisions and of the experimental environment at HERA. Special emphasis is put on extractions of α s values and on the influence of jet data on fits of the proton partondistribution functions. Where useful, the HERAresults are also discussed in the light of results from other colliders like LEP, the Tevatronor the LHC. The central message from these studies is that QCD does not only describe most of the measurements very well, but that QCD at HERAhas achieved the status of a precision theory. On the other hand it is shown that further understanding of problematic issues relies critically on theoretical progress in the form of improved models or of increased precision in analytical calculations.